1. Field of the Invention
The present invention relates to a piercing needle which is temporarily indwelled in a blood vessel in performing, e.g., blood transfusion or fluid therapy.
2. Description of the Related Art
Conventionally, when blood transfusion or fluid transfusion, for example, is to be performed into a blood vessel, a piercing needle is pierced into a blood vessel with its inner and outer needles assembled together. Thereafter, only the inner needle is pulled out, and a connector of, e.g., a blood transfusion set (or a fluid therapy set) is connected to an outer needle hub, thereby performing the operation of interest. However, during the manipulation of pulling out the inner needle and connecting the connector, blood may leak from the outer needle hub. In order to prevent this blood leakage, piercing needles in each of which a valve disc is provided in an outer needle hub have been conventionally proposed (Unexamined Published Japanese Patent Application Nos. 60-88562 and 63-197463).
In such a conventional puncturing needle incorporating a valve disc, however, when an inner needle is pulled out during a manipulation, air remaining in an outer needle hub cannot be vented due to the sealing properties of the valve disc itself. For this reason, the outer hub cannot be filled with blood, and this makes it impossible to confirm a so-called flashback in the outer needle hub unless a an especially cumbersome manipulation is performed.
To solve the above problems, Unexamined Published Japanese Patent Application No. 63-197463 proposes an injection device in which vent means is provided in the side wall of coupling means corresponding to the outer needle hub to vent air from the coupling means chamber and to prevent leakage of a liquid.
The vent means disclosed in the above proposal, however, adopts a structure in which a cylindrical hole is formed in the side wall of the coupling means and a cylindrical filter is fitted in the hole. Therefore, the manufacture of the puncturing needle is complicated and results in a high cost, and there is another disadvantage that the filter may be removed during the manufacture. In addition, during the blood vessel piercing manipulation, the filter portion may be closed with fingers, thus disenabling the reliable confirmation of a flashback. Furthermore, the vent means disclosed in the above proposal has a saddle for preventing blood from being brought into contact with air through the filter. This saddle is formed outside the coupling means and can slide to cover the film. However, this saddle mechanism also has a complicated structure, and this also results in a cumbersome manufacture or a complicated manipulation. In other words, the presence of the saddle may hinder the reliable and easy manipulation of the injection device.
In addition, since the position of the filter is separated from the position of the valve, air in the hub may remain between the filter and the valve disc.